The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Internal combustion engines combine air and fuel to create an air/fuel (A/F) mixture that is combusted within a plurality of cylinders. The combustion of the A/F mixture drives pistons which rotatably turns a crankshaft and generates drive torque. In compression ignition (CI) engines, air may be drawn into the cylinders and compressed by the pistons. Fuel may then be injected into the compressed air causing the pressurized A/F mixture to combust. For example, CI engines include diesel engines.
Exhaust gas produced during combustion may be expelled from the cylinders into an exhaust manifold. The exhaust gas may include carbon monoxide (CO) and hydrocarbons (HC). The exhaust gas may also include nitrogen oxides (NOx) due to the higher combustion temperatures of CI engines compared to spark ignition (SI) engines. An exhaust treatment system may treat the exhaust gas to remove CO, HC, and/or NOx. For example, the exhaust treatment system may include at least one of an oxidation catalyst (OC), NOx absorbers/adsorbers, a selective catalytic reduction (SCR) system, a particulate matter (PM) filter, and catalytic converters.
In the SCR process, a dosing agent is injected into the exhaust gas by a dosing system. For example, the dosing agent may be pure anhydrous ammonia, aqueous ammonia, or urea. The dosing agent includes a reductant that reacts with the NOx in the exhaust gas. For example, the reductant may be ammonia (NH3). The reductant mixes with the NOx in the exhaust gas and the mixture may be absorbed onto the SCR catalyst. The SCR catalyst may then break down the absorbed mixture forming water vapor (H2O) and nitrogen gas (N2). The SCR process, therefore, may significantly reduce NOx emissions.